High anisotropy alloy for thin film disk

ABSTRACT

The thin film disk of the invention includes a thin film pre-seed layer of amorphous or nanocrystalline structure. The pre-seed layer, which may be CrTa or AlTi or AlTa, is deposited prior to a first crystalline layer. Although the pre-seed layer may be amorphous or nanocrystalline, for brevity it will be referred to herein as amorphous which is intended to encompass a nanocrystalline structure. In the preferred embodiment of the present invention, a pre-seed layer is sputtered onto a nonmetallic substrate such as glass, followed by a ruthenium-aluminum (RuAl) layer with B2 structure. The use of the pre-seed layer improves grain size and its distribution, in-plane crystallographic orientation, coercivity (Hc) and SNR. In a preferred embodiment of the present invention, the pre-seed layer is followed by the RuAl seed layer, a Cr alloy underlayer, an onset layer and a magnetic layer. The amorphous pre-seed layer also allows use of a thinner RuAl seed layer which results in smaller overall grain size, as well as, a reduction in manufacturing cost due to relatively high cost of ruthenium. The increased coercivity also allows the use of a thinner Cr alloy underlayer, which also results in smaller overall grain size. Another benefit lies in the fact that the pre-seed layer provides additional thermal conductivity, which could help prevent thermal erasures on a glass disk. A cobalt based magnetic layer with an optimal concentration of Pt, B and Cr is also used to form the magnetic layer. Such an optimization produces high anisotropy, low noise, high coercivity and smaller grain size of the magnetic layer.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/500,710, filed on Feb. 9, 2000, and entitled“NON-METALLIC THIN FILM MAGNETIC RECORDING DISK WITH PRE-SEED LAYER”.

BACKGROUND OF THE INVENTION

[0002] The use of a RuAl seed layer, which is included in the preferredembodiment discussed below, is described in a commonly assigned,co-pending U.S. patent application with Ser. No. 09/295,267. The use ofan onset layer, which is included in the preferred embodiment discussedbelow, is described in a commonly assigned, co-pending U.S. patentapplication with Ser. No. 08/976,565 entitled “Thin Film Disk with OnsetLayer.” U.S.P.T.O application Ser. No. 09/020,151, entitled “THIN FILMMAGNETIC DISK HAVING REACTIVE ELEMENT DOPED REFRACTORY METAL SEED LAYER”is mentioned below.

[0003] 1. Field of the Invention

[0004] This invention relates generally to the field of thin filmmaterials used in magnetic disks for data storage devices such as diskdrives. More particularly the invention relates to the use of a highanisotropy alloy to form the magnetic layer on a thin film disk.

[0005] 2. Background of the Invention

[0006] The magnetic recording disk in a conventional drive assemblytypically consists of a substrate, an underlayer consisting of a thinfilm of chromium (Cr) or a Cr alloy, a cobalt-based magnetic alloydeposited on the underlayer, and a protective overcoat deposited on themagnetic layer. A variety of disk substrates such as NiP-coated AlMg,glass, glass ceramic, glassy carbon etc., can be used. Disks that arecommonly available in the market are made with an AlMg substrate onwhich a layer of amorphous NiP is electrolessly deposited. While acoating on the substrate is important because such a coating givesuniform magnetic read-back signals during the course of a diskrevolution, the process of electroless deposition of NiP on an AlMgsubstrate has several disadvantages, one of them being the fact thatelectroless deposition is a wet process. The wet nature of the processnecessitates that it be performed quite separately from the sputteringprocess by which the remainder of the layers in a magnetic recordingdisk is deposited. A NiP layer has other disadvantages too. Forinstance, with a NiP layer, it is difficult to achieve the smoothnessand uniformity in the NiP surface of the magnetic recording disk, whichis a prerequisite for the high densities required in current diskdrives. Yet another problem associated with the NiP surface iscorrosion. The NiP surface also tends to limit the processingtemperatures because of its tendency to become magnetic if heated beyonda certain point.

[0007] Further, in cases where a non-metallic substrate such as glass ischosen, the conventional NiP coating is not preferable for use on glassas pre-seed layer for many reasons including those noted above. In suchcases, the non-metallic substrate disks typically have a so called “seedlayer” sputter deposited onto the substrate between the substrate andthe Cr-alloy underlayer. The selection of the seed layer allows theperformance of non-metallic substrates to exceed the magnetic recordingcharacteristics of NiP/AlMg disks because the seed layer of the magneticdisk drive influences nucleation and growth of the underlayer which inturn affects the recording characteristics of the magnetic layer.Several materials have been proposed in published papers for seed layerssuch as: Al, Cr, CrNi, Ti, Ni₃P, MgO, Ta, C, W, Zr, AlN and NiAl onglass and non-metallic substrates. (See for example, “Seed Layer induced(002) crystallographic texture in NiAl underlayers,” Lee, et al., J.Appl. Phys. 79(8), 15 April 1996, p.4902ff). In a single magnetic layerdisk, Laughlin, et al., have described use of a NiAl seed layer followedby a 2.5-nm thick Cr underlayer and a CoCrPt magnetic layer. The NiAlseed layer with the Cr underlayer was said to induce the [10{overscore(1)}0] texture in the magnetic layer. (“The Control and Characterizationof the Crystallographic Texture of Longitudinal Thin Film RecordingMedia,” IEEE Trans. Magnetic. 32(5) September 1996, 3632). In one of therelated applications noted above, the use of RuAl for a seed layer isdisclosed.

[0008] A Cr underlayer is mainly used to influence such microstructuralparameters as the preferred orientation (PO) and grain size of thecobalt-based magnetic alloy forming the onset layer. When the Crunderlayer is deposited at elevated temperature on a NiP-coated AlMgsubstrate a [100] PO is usually formed. A PO of the underlayer promotesthe epitaxial growth of [11{overscore (2)}0] PO of the hcp cobalt (Co)alloy forming the onset layer, thereby improving the in-plane magneticperformance of the disk for longitudinal recording. The [11{overscore(2)}0] PO refers to a film of hexagonal structure whose (11{overscore(2)}0) planes are predominantly parallel to the surface of the film.Since nucleation and growth of Cr or Cr alloy underlayers on glass andmost non-metallic substrates differ significantly from those onNiP-coated AlMg substrates, different materials and layer structures areused on glass substrate disks to achieve optimum results.

[0009] The design of magnetic disks has advanced rapidly in recent yearsand even 1 dB improvement in the Signal-to-Noise Ratio (SNR) is nowconsidered quite significant. Recording density of magnetic disks ashigh as 30 to 40 gigabits per square inch has been achieved in theindustry; however, this density has only been achieved in the laboratoryand the density found in state of the art commercially available diskdrives is far below this value. The recording density of a disk is alsodependent on the thermal stability of the recorded information on thedisk because a commercially viable disk drive must be capable ofmaintaining the stored information for periods of time measured inyears.

[0010] The use of Co alloys to form the magnetic layer of a magneticdisk has been discussed by Ishikawa et al. in Magn, Mater, 152 pp265-273 (1996). The article mentions that the density of stacking faultsincreases with addition of Pt in CoPtCr. A maximum in coercivity wasobserved at 12 at % Pt. At higher Pt concentrations, the decrease inmagnetocrystalline anisotropy (Ku) due to stacking faults and formationof FCC phase overcomes the increase in Ku associated with higher Ptconcentration in the lattice.

[0011] Similarly, Inaba et al. in IEEE. Trans, Magn 34, pp 1558-1560(1990) have discussed that the use of Cr in the magnetic layer decreasesthe Ku of Co alloys. However, Cr is added because of its tendency tosegregate to the grain boundaries and magnetically isolate the grains.Therefore, a need exists for an optimization of the desiredconcentration of metals forming the magnetic layer alloy of a disk so asto increase coercivity and reduce stacking faults.

SUMMARY OF INVENTION

[0012] The thin film disk of the invention includes a thin film pre-seedlayer of amorphous or nanocrystalline structure. The pre-seed layerwhich may be CrTa or AlTi or AlTa, is deposited prior to a firstcrystalline layer. Although the pre-seed layer may be amorphous ornanocrystalline, for brevity it will be referred to herein as amorphouswhich is intended to encompass a nanocrystalline structure. In thepreferred embodiment of the present invention, a pre-seed layer issputtered onto a non-metallic substrate such as glass, followed by aruthenium-aluminum (RuAl) seed layer with B2 structure. The use of thepre-seed layer improves grain size and its distribution, in-planecrystallographic orientation, coercivity (Hc) and SNR. In a preferredembodiment of the present invention, a pre-seed layer is followed by theRuAl seed layer, a Cr alloy underlayer, an onset layer and a magneticlayer. The amorphous pre-seed layer also allows use of a thinner RuAlseed layer which results in smaller overall grain size, as well as, areduction in manufacturing cost due to relatively high cost ofruthenium. The increased coercivity also allows the use of a thinner Cralloy underlayer, which also results in smaller overall grain size.Another benefit lies in the fact that the pre-seed layer providesadditional thermal conductivity, which could help prevent thermalerasures on a glass disk. A cobalt based magnetic layer with an optimalconcentration of Pt, B and Cr is also used to form the magnetic layer.Such an optimization produces high anisotropy, low noise, highcoercivity and smaller grain size of the magnetic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a top view of a disk drive illustrating the structuralcomponents of a disk drive with a rotary actuator as used in the presentinvention.

[0014]FIG. 2 is a diagram illustrating the layer structure of a thinfilm magnetic disk according to a preferred embodiment of the presentinvention.

[0015]FIG. 3 is a graph illustrating the x-ray diffraction data forvarious samples of a magnetic disk drive showing the structuralvariations of CrTa with changes in composition.

[0016]FIG. 4 is a graphical illustration showing x-ray diffraction datafor samples of thin film magnetic disks showing the structuralvariations of materials with changes in thickness of a CrTa₅₀ pre-seedlayer according to the invention.

[0017]FIG. 5 is a graphical illustration showing x-ray diffraction datafor samples of thin film magnetic disks showing the structuralvariations of the materials with changes in thickness of a AlTi₅₀ thinfilm layer according to a preferred embodiment of the present invention.

[0018]FIG. 6 is a graphical depiction of the relationship betweenremanent coercivity and varying concentrations of Pt in the magneticlayer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0019]FIG. 1 is a top view illustrating a disk drive with a rotaryactuator in which a thin film disk according to a preferred embodimentof the present invention may be used. The disk drive system includes oneor more magnetic recording disks 111 mounted on a spindle 112, which isrotatable by an in-hub electrical motor (not shown). An actuatorassembly 115 supports a slider 120, which contains one or moreread/write heads. The actuator assembly 115 is composed of a pluralityof actuators and sliders arranged in a vertical stack with the actuatorssupporting the sliders being in contact with the surfaces of the diskswhen the disks are not rotating or being unloaded to avoid contact. Avoice coil motor (VCM) 116 moves the actuator assembly 115 relative tothe disks by causing the assembly to pivot around a shaft 117. Theread/write heads are typically contained in air bearing sliders adaptedfor flying above the surface of the disks when rotating at a sufficientspeed. During the operation of the disk drive, if the sliders fly abovethe disks the VCM moves the sliders in an arcuate path across the disksso as to allow the heads to be positioned to read and write magneticinformation from the circular tracks which are formed in the data area114. The data area is coated with thin films as described below.Electrical signals to and from the heads and the VCM are carried by aflex cable 118 to drive electronics 119. When the disk drive is notoperating and during such periods of time as when the rotation of thedisks is either starting or stopping, the sliders may either be removedfrom the disks using load/unload ramps (not shown) or parked in physicalcontact with the surface of the disks in a landing zone or contactstart/stop (CSS) area 113, which is not used for data storage eventhough the magnetic coating extends over this area. If the sliders areunloaded from the disks during non-operation, there is no need to have aCSS area and more of the disk becomes available for data storage.Although the disk drive has been described with air bearing sliders thedisk of the present invention may easily be used in other storagedevices having near contact, or contact recording sliders.

[0020]FIG. 2 is a diagram illustrating the layer structure of a thinfilm magnetic disk according to a preferred embodiment of the presentinvention. The thin film layers are deposited onto at least one andpreferably both planar surfaces of the magnetic disk to form the datarecording area. The substrate 10 may be made of glass or any othersuitable material.

[0021] A CrTa or AlTi or AlTa pre-seed layer 12 is first deposited ontothe substrate. The pre-seed layer is deposited by conventional DCmagnetron sputtering. The composition of the pre-seed layer is selectedto produce a film with an amorphous or nanocrystalline structure. Theuse of a pre-seed layer improves the media coercivity for a filmstructure with very thin RuAl seed layer and ultra-thin Cr alloyunderlayer.

[0022] The RuAl seed layer 14 is next deposited directly onto thepre-seed layer. The seed layer could also be a “double layer” with alayer of RuAl followed by a layer of NiAl, for example. This doublelayer configuration could result in cost savings by reducing the amountof Ru required. Ru is an expensive element, so a reduction in therequired quantity of Ru will reduce the costs. In the double layerstructure the RuAl seed layer establishes the grain size and orientationand the subsequently deposited NiAl follows the established patterns. Anunderlayer 16 is next deposited onto the seed layer 14 and is comprisedof a non-ferromagnetic material such as a chromium alloy e.g CrV orCrTi. The underlayer 16 is followed by a Co-alloy onset layer 18 and aCoPtCrB magnetic layer 20. The use of an onset layer 18 is described ina commonly assigned, co-pending U.S. patent application with Ser. No.08/976,565. Typically, the onset layer material is selected in part forits lattice match with the underlayer. Lattice parameters, which areintermediate between that of the underlayer 16 and the magnetic layer 20may strengthen the epitaxy of the grains in the desired orientation. Thepreferred onset layer 18 is of hexagonal close packed (hcp) structuredferromagnetic material. Materials, which are suitable to form the onsetlayer, include a wide range of cobalt alloys such as CoNiCr, CoCrTa,etc. Nonmagnetic materials such as CoCr (Cr>30 at. %) can also be usedas onset layers. An onset layer 18 is typically 1-4 nm thick.

[0023] A preferred embodiment of the present invention has a magneticlayer 20 deposited on the onset layer. The magnetic layer is an alloy ofcobalt, which typically contains platinum and chromium and may containadditional elements such as tantalum or boron, e.g. CoPtCrTa or CoPtCrB.A typical magnetic layer might comprise 12 to 20 at. % platinum, 16 to20 at. % chromium and 6 to 10 at. % boron with cobalt forming theremainder of the magnetic layer. In accordance with a preferredembodiment of the present invention, the thickness of the magnetic layercan be from 5-30 nm with 10-20 nm being the preferred thickness range.The use, composition and thickness of an overcoat 22 are not critical inpracticing the invention, but a typical thin film disk might use anovercoat less than 15 nm thick.

[0024] While the compositions listed above have been given withoutregard to contamination percentages, it is known to those skilled in theart that some contamination is normally, if not always, present in thinfilms. Sputtering targets are typically specified as 99.9% or greaterpurity, but the resulting films may have much lower purity due tocontamination in the sputtering chamber or other factors. For example,contamination by air in the chambers might result in measurable amountsof oxygen and/or hydrogen being incorporated into the film. It is alsoknown that some small amount of oxygen is normally found in Cr targetsand in the resulting Cr layer. It is also possible for small amounts ofthe working gas in the sputtering system, e.g. argon, to be incorporatedinto a sputtered film. Contamination levels were not specificallymeasured in the disk samples described and, therefore, were assumed tobe within normal ranges for sputtered thin film disks expected by thoseskilled in the art.

[0025] The thin film disk made according to the invention can be usedfor storing data in typical disk drives using either magnetoresistive orinductive heads and can be used in contact recording or with flyableheads. The read/write head is positioned over the rotating disk in astandard manner to either record or read data.

[0026] In general, the application of some type of seed layer on glassand other alternate substrates to control nucleation andcrystallographic orientation of the Cr (or Cr alloys), and thereby themagnetic Co-alloy layer is well known. U.S. Pat. No. 5,789,056 disclosedthat the use of a very thin seed layer and underlayer on glass mediareduce the grain size of magnetic alloy substantially, thereby improvingSNR. By applying different compositions of seed layers,crystallographically textured (112) or (100) Cr layer can be deposited.By sputtering Co-alloys on these Cr underlayers, textures of either(10{overscore (1)}0) or (11{overscore (2)}0) in the magnetic layer canbe achieved. For high deposition rate sputtering, it has been found thatthe application of an amorphous TaN seed layer on glass induces a (100)orientation in the subsequently grown Cr underlayer, which promotes astrong (11{overscore (2)}0) orientation in the Co-alloy layer. (SeeU.S.P.T.0 application Ser. No 09/020,151, filed: Feb. 6, 1998, THIN FILMMAGNETIC DISK HAVING REACTIVE ELEMENT DOPED REFRACTORY METAL SEEDLAYER). However, the formation of TaN layer requires a reactiveatmosphere in the sputtering chamber and, therefore, increases thedifficulty encountered in sputtering. The (11{overscore (2)}0) textureof a Co-alloy layer can also be obtained by depositing a relativelythick RuAl seed layer, but the high cost of RuAl sputtering targets is amajor drawback for its use in large scale manufacturing. The use of aCrTa pre-seed layer allows the use of a very thin RuAl seed layer (andthus reduces cost) and an ultra-thin Cr (or Cr-alloys) underlayer on aglass substrate, which in turn enables the subsequent growth of strong(11{overscore (2)}0) oriented Co-alloy onset layer with controlledsmaller grain size.

[0027] In accordance with a preferred embodiment of the presentinvention, the pre-seed layer 12 is sputter deposited onto a glasssubstrate 10 followed by a thin RuAl seed layer 14, an ultra-thinCr-alloy underlayer 16, a Co-alloy onset layer 18 and a CoPtCrB magneticlayer 20. In order to enhance the lattice match between the RuAl seedlayer and the Cr-alloy underlayer, CrTi or CrMo alloys may be preferredto form the underlayer. A CrMo underlayer is also advantageous becauseit helps render the SNR less sensitive to changes in the thickness ofthe underlayer. Magnetic properties and SNR data for disks with andwithout a CrTa and AlTi pre-seed layer are listed in Table-1 for acomparison. TABLE 1 Hc SoNR Disk Structure (Oe) Mrt S* (dB) 1RuAl₅₀/CrTi₁₀/CoCr₃₇/CoPt₁₁Cr₂₀B₇ 3040 0.375 0.66 27.6 2CrTa₅₀/RuAl₅₀/CrTi₁₀/CoCr₃₇/CoPt₁₁Cr₂₀B₇ 3660 0.420 0.80 27.7 3NiAl₅₀/CrV₂₀/CoCr₃₇/CoPt₁₀Cr₂₀B₆ 3400 0.420 0.78 26.4 4AlTi₅₀/RuAl₅₀/CrTi₁₀/CoCr₃₇/CoPt₁₁Cr₂₀B₇ 3500 0.430 0.81 27.7

[0028] The data in table 1 shows that although disks 1 and 2 have acomparable SoNR, disk 2 with a CrTa₅₀, i.e., 50 at. % Ta, pre-seed layerexhibits a substantially higher Hc and coercive squareness S*. At thesame Mrt (remanent magnetization times thickness) as disk 3, disk 2gives rise to a SoNR improvement of 1.3 dB as compared to the NaAl₅₀seed layer structure of disk 3. Disk 4, which was made with an AlTi₅₀pre-seed layer, also shows an improved performance over the prior artNiAl₅₀ (disk 3). The high coercivity and squareness achieved with CrTaand AlTi pre-seed layers is a result of creating the enhanced RuAl <100>and in-plane Co <11{overscore (2)}0> textures.

[0029]FIG. 3 is a graph illustrating the X-ray diffraction data forvarious samples of a magnetic disk drive showing the structuralvariations of CrTa with different changes in composition. The figureshows spectra for a set of film structures with CrTa₅₀, CrTa₂₀, CrTa₁₀,CrTa₂ and Ta only pre-seed layers. No significant peaks appear for theCrTa₅₀ film indicating that this composition results in a substantiallyamorphous or nanocrystalline film. Both the pure Ta and CrTa₂₀ filmsresult in significant diffraction peaks indicating crystallinestructure.

[0030]FIG. 4 is a graphical illustration showing X-ray diffraction datafor samples of thin film disks made with varying thickness of CrTa₅₀pre-seed layers ranging from 0 to 45 nm. The results are believed to beconsistent up to a thickness of 60 nm. Throughout the X-ray spectra nocrystalline CrTa diffraction peaks are observed, thus confirming theamorphous nature of the pre-seed layer. As is known to those of ordinaryskill in the art, the use of RuAl seed layer on glass substrate createsa Cr <200> texture, which leads to a <11{overscore (2)}0> texture in theCo-alloy layer. For a film structure without the CrTa pre-seed layer,all the diffraction peak intensities are very weak, indicating poorstructural integrity due to the deposition of very thin RuAl seed layerand CrTi underlayer directly on glass. By depositing a CrTa pre-seedlayer, substantial enhancements of RuAl (100), (200), CrTi (200) andCo-alloy (11{overscore (2)}0) diffraction peaks are observed, indicatinga significant improvement of the C-axis in-plane orientation.

[0031]FIG. 5 shows X-ray diffraction plots for disks made with 0, 150,300 and 450 Angstroms of thicknesses of AlTi₅₀ pre-seed layers. Theresults are believed to be valid down to a thickness of 100 Angstroms(A), i.e. 10 nm. The disks had RuAl seed layers, CrTi underlayers andcobalt alloy magnetic layers. The graph shows that the preferredorientations of RuAl (100), RuAl (200), CrTi (200) and Co (11{overscore(2)}0) strengthen with increased thickness of the AlTi pre-seed layer.As shown in FIG. 3 the preferred composition for the CrTa pre-seed layeris CrTa₅₀. The behavior of AlTi is similar to CrTa in this respect, sothe preferred composition for an AlTi is also 50-50.

[0032] Table 2 summarizes the values of full width half-maximum (FWHM)derived from the RuAl (200) and Co (11{overscore (2)}0) peaks. It isclear that the much smaller FWHM values are measured for the filmstructure with either CrTa₅₀ or AlTi₅₀ pre-seed layers. The smaller FWHMvalues indicate a high degree of in-plane texture and less dispersion of[11{overscore (2)}0] preferred orientation of the hexagonal Costructure. TABLE 2 Film structure RuAl (200) (° F.WHM) Co(1{overscore(12)}0)(° F.WHM) RuAl₅₀/CrTi₁₀/CoCr/CoPtCrB 17.6 12.8 CrTa₅₀/RuAl₅₀/CrTi₁₀/CoCr/CoPtCrB  5.8 5.2AlTi₅₀/RuAl₅₀/CrTi₁₀/CoCr/CoPtCrB  8.7 6.8AlTa₂₀/RuAl₅₀/CrTi₁₀/CoCr/CoPtCrB 11.6 8.8

[0033] It is also known that the poor thermal conductivity of glasssubstrates can cause the recorded data bits to be thermally erased. Theuse of a relatively thick CrTa pre-seed layer could potentially havesome advantage in addressing the thermal erasure issue related to aglass disk medium.

[0034] Use of sputtered NiP pre-seed layer together with a Cr sub-seedlayer and a NiAl seed layer was published by Chen, Yen, Ristau, Ranjan.(“Effect of Cr sub-seed layer thickness on the crystallographicorientation of Co-alloy recording media on glass,” IEEE Trans. Magn. 35,pp. 2637-2639 (1999). Their results showed that (11{overscore (2)}0)Co-alloy texture can be generated for thicker (>45 Å) Cr sub-seedlayers, but the SNR was poor due to larger grain size. For thin Crsub-seed layers, the use of the NiAl seed layer induces (10{overscore(1)}0) Co-alloy texture.

[0035] RuAl tends to form the B2 (cesium chloride) structure in asputtered thin film. Small amounts of other materials could conceivablybe added to RuAl without disrupting the critical B2 structure. The B2structure is an ordered cubic structure that can be described as twointerpenetrating simple cubic lattices where, for RuAl, Al atoms occupyone lattice and Ru atoms the other. RuAl has a lattice constant, whichis close to that of Cr even though Cr has a bcc structure. RuAl tends toform smaller grain size than Cr due to the strong bonding between the Ruand Al atoms, which reduces atomic mobility during deposition.

[0036] The role of the RuAl layer of the preferred embodiment ofinvention is to ultimately control the orientation, grain size and grainsize distribution of magnetic grains. The grain size and orientationachieved in a RuAl layer is propagated into the magnetic layer throughepitaxial growth of properly selected subsequent layers including themagnetic layer. Whereas the traditional thin film magnetic disk has onlythree layers e.g., underlayer, magnetic layer and overcoat, the trend inthe industry is towards using additional layers. The terminology forthese additional layers has not become standardized, but in adescriptive sense, there may be pre-seed layers 12, seed layers 14, oneor more underlayers 16, non-magnetic or magnetic onset layers 18, aplurality of magnetic layers 20 which may or may not have spacers layersseparating them. In addition what is called the “substrate” 10 may infact be multilayered material. In this context of proliferating layers,the RuAl seed layer can be effective in achieving the beneficial resultsdescribed herein so long as it is deposited in the B2 structure andahead of the magnetic layer. Thus, the RuAl seed layer in the preferredembodiment is intended to be the first non-amorphous layer to influencecrystallographic orientation and grain size of subsequently depositedmagnetic material.

[0037] In a preferred embodiment of the invention, the CrTa or AlTipre-seed layer is sputter deposited onto the substrate (which mayalready have thin films on it) from targets composed substantially of(a) CrTa and preferably CrTa₅₀, or (b) AlTi and preferably AlTi₅₀. TheRuAl seed layer 14 is deposited onto the pre-seed layer 12 by standardsputtering techniques.

[0038] In accordance with a preferred embodiment of the presentinvention, the magnetic layer 20 is an alloy of cobalt, which typicallycontains Pt and Cr and may contain additional elements such as tantalumand boron, e.g CoPtCrTa or CoPtCrB. A typical magnetic layer mightcomprise 12 to 20 at. % platinum, 16 to 20 at. % chromium and 6 to 10at. % boron with cobalt forming the remainder of the magnetic layer.

[0039] As is known to those of ordinary skill in the art, KuV/kT<60indicates low stability, where

[0040] Ku=Magnetocrystalline anisotropy,

[0041] V=Switching volume,

[0042] k=Boltzmann's constant; and

[0043] T=absolute temperature.

[0044] In order to improve stability of the magnetic disk, the wholeratio of KuV/kT needs to be raised. Raising of the ratio can be achievedby increasing magnetocrystalline anisotropy (Ku), which in turn raisescoercivity (Hc) because Ku is a function of Hc. Thus, by raising Ku,coercivity is increased and so is stability of the magnetic disk. Thefollowing table illustrates the use of a higher concentration of Pt inthe magnetic layer to increase Hc and also Ku resulting in an improvedstability of the magnetic disk. TABLE 3 Magnetic Layer Pt Concentration(at. %) Remanent Coercivity (Oe) A 12 4000 B 14 4400 C 16 4800 D 18 4780E 20 4900

[0045] A comparison of different magnetic layers with varyingconcentrations of Pt is presented in table 3. As can be understood fromtable 3, the presence of Pt in the magnetic layer has the tendency toraise the coercivity (Hc) of Co alloys and also magnetocrystallineanisotropy (Ku) of the magnetic layer. Therefore, a higher Ptconcentration is generally used in the magnetic layer so as to raise Hcof the magnetic layer. The relationship between remanent coercivity andvarying Pt concentrations in the magnetic layer is graphically depictedin FIG. 6 for two magnetic layers having differing MrT values. Asdepicted therein, the remanent coercivity Hc (Oe) of the magnetic layer20 generally increases with an increase in the concentration of Pt inthe magnetic layer for alloys containing 18 at. % Cr and 8 at. % boron.The difference in coercivity at different values of MrT is a measure ofthermal stability and such difference indicates that the higher Ptconcentration alloys are more thermally stable (less change incoercivity with MrT as Pt increases).

[0046] However, increasing the concentration of Pt in the magnetic layerbeyond a certain range tends to result in the formation of stackingfaults in the magnetic layer. Typically, spheres of atoms forming acrystal structure in any given layer of a disk are arranged in a singleclose packed layer A by placing each sphere in contact with six others.A second similar layer B is added by placing each sphere of atoms oflayer B in contact with three spheres of the bottom layer. A facecentered cubic (fcc) structure of a crystal is formed when the spheresof the third layer C are added over the holes in the first layer thatare not occupied by layer B spheres to form a configuration of ABC, ABC.A hexagonal close packed (hcp) structure of a crystal is obtained whenthe spheres in the third layer are placed directly over the centers ofthe spheres in the first layer to form a configuration of AB, AB, AB.Where the Pt concentration in the magnetic layer is increased beyond 20at. % stacking faults tend to appear in the magnetic layer resulting ina configuration of ABC, AB, AB, which is undesirable.

[0047] In order to circumvent these problems, boron is added to themagnetic layer. The addition of boron to the magnetic layer helps reducestacking faults. Boron also helps in preventing the formation of theundesirable fcc crystal structure and helps in inducing hcp crystalstructures, which are the desirable crystal structures. Boron also helpssupport a further increase in the concentration of Pt in the magneticlayer while still helping in maintaining an increase in coercivity ofthe magnetic layer.

[0048] Boron also helps to reduce the amount of magnetic exchange andcoupling between grains in the magnetic layer. The magnetic cluster sizein the media determines the level of noise. In the case where the grainsare completely isolated magnetically from each other, the cluster sizeis equal to the grain size. When exchange coupling is present betweengrains, the magnetic cluster size increases and the SNR is degraded.Since Boron segregates to grain boundaries, it acts to reduce couplingbetween grains in the magnetic layer and improve SNR. Boron alsoimproves SNR through decrease of the grain size in the magnetic layer.

[0049] An increase in the concentration of Pt in the magnetic layerallows more of boron to be dissolved in the crystal lattices of themagnetic layer. Therefore, the boron concentration in the magnetic layercan be increased, corresponding to increases in Pt concentration in themagnetic layer, without disrupting the epitaxial growth of the magneticlayer on the onset layer. In accordance with a preferred embodiment ofthe present invention, the composition of the magnetic layer isCoPt_(x)Cr₁₈B_(y) where x>4+y, and where x=at. % of Pt and y=at. % ofboron.

[0050] Cr is a desirable component of the magnetic layer because itdecreases noise due to its tendency to segregate grains in the magneticlayer. However, addition of Cr decreases Ku so it is desirable to use anoptimal concentration of Cr needed to isolate the grains in the magneticlayer. Since boron and Cr have similar properties in regard to coupling,boron and Cr are added to the magnetic layer.

[0051] While the preferred embodiments of the present invention havebeen illustrated in detail, it will be apparent to the one skilled inthe art that alternative embodiments of the invention are realizablewithout deviating from the scope and spirit of the invention.

What is claimed is:
 1. A thin film magnetic disk comprising: asubstrate; a pre-seed layer with an amorphous or nanocrystallinestructure; a non-magnetic ruthenium-aluminum (RuAl) seed layer depositedover the pre-seed layer; at least one non-magnetic underlayer depositedover the RuAl seed layer; at least one onset layer deposited over theunderlayer; and at least one magnetic layer deposited over the onsetlayer, wherein said magnetic layer alloy is comprised ofCoPt_(x)CrB_(y), wherein x is the at. % concentration of Pt, y is theat. % concentration of boron, and x>4+y.
 2. The disk of claim 1 ,wherein the Pt concentration in the magnetic layer is in the range of12-20 at. %.
 3. The disk of claim 1 , wherein the Cr concentration inthe magnetic layer is in the range of 16-20 at. %.
 4. The disk of claim1 , wherein the boron concentration in the magnetic layer is in therange of 6 to 10 at. %.
 5. The disk of claim 1 , wherein the pre-seedlayer is CrTa and contains approximately 50 at. % Ta.
 6. The disk ofclaim 1 , wherein the pre-seed layer is AlTi and contains approximately50 at. % Ti.
 7. The disk of claim 1 , wherein the pre-seed layer is AlTaand contains approximately 20 at. % Ta.
 8. The disk of claim 1 , whereinthe thickness of the pre-seed layer is greater than or equal to 10 nm.9. The disk of claim 1 , wherein the thickness of the pre-seed layer isless than or equal to 60 nm.
 10. The disk of claim 1 , wherein the RuAlseed layer is between 3 and 20 nm in thickness.
 11. The disk of claim 1, wherein the RuAl seed layer has a B2 structure.
 12. The disk of claim1 , wherein the RuAl seed layer has a <200> preferred orientation. 13.The disk of claim 1 , wherein the underlayer is a chromium alloycontaining approximately 10 at. % titanium.
 14. The disk of claim 1 ,wherein the underlayer comprises CrTi with a <200> preferredorientation.
 15. The disk of claim 1 , wherein the underlayer comprisesCrTi and is between 3 and 15 nm in thickness.
 16. The disk of claim 1 ,wherein the onset layer comprises an alloy of CoCr.
 17. A disk drivecomprising: a motor for rotating a spindle; a thin film magnetic diskmounted on the spindle; and an actuator assembly including a head forwriting magnetic information on the disk as it rotates, wherein saidthin film disk includes: a substrate; a pre-seed layer with an amorphousor nanocrystalline structure; a non-magnetic ruthenium-aluminum (RuAl)seed layer deposited over the pre-seed layer; at least one non-magneticunderlayer deposited over the RuAl seed layer; at least one onset layerdeposited over the underlayer; and at least one magnetic layer depositedover the onset layer, wherein said magnetic layer alloy is comprised ofCoPt_(x)CrB_(y), wherein x is the at. % concentration of Pt, y is theat. % concentration of boron, and x>4+y.
 18. The disk drive of claim 17, wherein the Pt concentration in the magnetic layer is in the range of12-20 at. %.
 19. The disk drive of claim 17 , wherein the Crconcentration in the magnetic layer is in the range of 16-20 at. %. 20.The disk drive of claim 17 , wherein the boron concentration in themagnetic layer is in the range of 6 to 10 at. %.
 21. The disk drive ofclaim 17 , wherein the pre-seed layer is CrTa and contains approximately50 at. % Ta.
 22. The disk drive of claim 17 , wherein the pre-seed layeris AlTi and contains approximately 50 at. % Ti.
 23. The disk drive ofclaim 17 , wherein the pre-seed layer is AlTa and contains approximately20 at. % Ta.
 24. The disk drive of claim 17 , wherein the thickness ofthe pre-seed layer is greater than or equal to 10 nm.
 25. The disk driveof claim 17 , wherein the thickness of the pre-seed layer is less thanor equal to 60 nm.
 26. The disk drive of claim 17 , wherein the RuAlseed layer is between 3 and 20 nm in thickness.
 27. The disk drive ofclaim 17 , wherein the RuAl seed layer has a B2 structure.
 28. The diskdrive of claim 17 , wherein the RuAl seed layer has a <200> preferredorientation.
 29. The disk drive of claim 17 , wherein the underlayer isa chromium alloy containing approximately 10 at. % titanium.
 30. Thedisk drive of claim 17 , wherein the underlayer comprises CrTi with a<200> preferred orientation.
 31. The disk drive of claim 17 , whereinthe underlayer comprises CrTi and is between 3 and 15 nm in thickness.32. A method of manufacturing a thin film magnetic disk comprising thesteps of: depositing a thin film pre-seed layer with an amorphous ornanocrystalline structure onto a substrate; depositing a crystallineruthenium-aluminum (RuAl) seed layer over the pre-seed layer; depositingat least one non-magnetic underlayer over the RuAl seed layer;depositing at least one onset layer over the underlayer; and depositingat least one magnetic layer over the onset layer, wherein said magneticlayer alloy is comprised of CoPt_(x)CrB_(y) wherein x is the at. %concentration of Pt, y is the at. % concentration of boron, and x>4+y.33. The method of claim 32 , wherein the Pt concentration in themagnetic layer is in the range of 12-20 at. %.
 34. The method of claim32 , wherein the Cr concentration in the magnetic layer is in the rangeof 16-20 at. %.
 35. The method of claim 32 , wherein the boronconcentration in the magnetic layer is in the range of 6 to 10 at. %.36. The method of claim 32 , wherein the pre-seed layer is CrTa andcontains approximately 50 at. % Ta.
 37. The method of claim 32 , whereinthe pre-seed layer is AlTi and contains approximately 50 at. % Ti. 38.The method of claim 32 , wherein the pre-seed layer is AlTa and containsapproximately 20 at. % Ta.
 39. The method of claim 32 , wherein thethickness of the pre-seed layer is greater than or equal to 10 nm. 40.The method of claim 32 , wherein the thickness of the pre-seed layer isless than or equal to 60 nm.
 41. The method of claim 32 , wherein theRuAl seed layer is between 3 and 20 nm in thickness.
 42. The method ofclaim 32 , wherein the RuAl seed layer has a B2 structure.
 43. Themethod of claim 32 , wherein the RuAl seed layer has a <200> preferredorientation.
 44. The method of claim 32 , wherein the underlayercomprises CrTi and is between 3 and 15 nm in thickness.
 45. The methodof claim 32 , wherein the underlayer is a chromium alloy containingapproximately 10 at. % titanium.
 46. The method of claim 32 , whereinthe underlayer comprises CrTi with a <200> preferred orientation. 47.The method of claim 32 , wherein thickness of the onset layer is in therange of 0.5 to 2.5 nm.